Is this move meant to be like a retention vanish and take place in the hand or should the move be done while coming down to the hand your pretending to put it in.

Generally, the thumb-palming of the coin should be done under cover of the hand. But you can bend the fingers inward a little bit on the way. If you thumb palm it on the way to put it into your hand, it looks suspicious, like you just did a move.

alright, thanks much

if someone could hit me up with a link to a good performance of a thumb palm it would be appreciated